1. Field of the Invention
The present invention relates to an electrophoretic display device and method of fabrication thereof.
2. Description of the Related Art
An electrophoretic display device is an image display device using a phenomenon that colloidal particles move to either one of the polarities when one pair of electrodes to which a voltage is applied are immersed into a colloidal solution. Contrary to a liquid crystal display device, such an electrophoretic display device has the advantage of wide viewing angle, high reflectivity, low power consumption, and the like, without using a backlight and thus it is widely used as an electronic device such as an electronic paper.
The electrophoretic display device has a structure in which an electrophoretic layer is interposed between two substrates. One of the two substrates is made of a transparent substrate and the other substrate is configured with an array substrate formed with a driving element to display images in a reflective mode in which light entering from the outside of the device is reflected.
FIG. 1 is a view illustrating the structure of an electrophoretic display device 1 in the related art. As illustrated in FIG. 1, the electrophoretic display device 1 may include a first substrate 20 and a second substrate 40, thin-film transistors and a pixel electrode 18 formed on the first substrate 20, a common electrode 42 formed on the second substrate 40, an electrophoretic layer 60 formed between the first substrate 20 and the second substrate 40, and an adhesive layer 56 formed between the electrophoretic layer 60 and the pixel electrode 18.
The thin-film transistor may include a gate electrode 11 formed on the first substrate 20, a gate insulation substrate 22 formed over the overall first substrate 20 formed with the gate electrode 11, a semiconductor layer 13 formed on the gate insulation substrate 22, and a source electrode 15 and a drain electrode 16 formed on the semiconductor layer 13. A passivation layer 24 is formed on the source electrode 15 and drain electrode 16 of the thin-film transistor.
The pixel electrode 18 for applying a signal to the electrophoretic layer 60 is formed on the passivation layer 24. Here, a contact hole 28 is formed on the passivation layer 24, and the pixel electrode 18 is connected to the drain electrode 16 of the thin-film transistor through the contact hole 28.
Furthermore, a common electrode 42 is formed on the second substrate 40 and an electrophoretic layer 60 is formed on the common electrode 42. Here, an adhesive layer 56 is formed on the electrophoretic layer 60 to attach the second substrate 40 including the electrophoretic layer 60 to the first substrate 20. The electrophoretic layer 60 may include a capsule 70 filled with white particles 74 and black particles 76 having an electrophoretic characteristic therein. When a signal is applied to the pixel electrode 18, an electric field is generated between the common electrode 42 and the pixel electrode 18, and white particles 74 and black particles 76 inside the capsule 70 are moved in a direction of the common electrode 42 or pixel electrode 18 by the electric field, thereby implementing an image.
For example, when a negative (−) voltage is applied to the pixel electrode 18 on the first substrate 20 and a positive (+) voltage is applied to the common electrode 42 on the second substrate 40, the positive (+) charged white particles 74 are moved to the side of the first substrate 20 and the negative (−) charged black particles 76 are moved to the side of the second substrate 40. In this state, when light is incident from the outside, i.e., an upper portion of the second substrate 40, incident light is reflected by the black particles 76, thereby implementing black on the electrophoretic display device.
On the contrary, when a positive (+) voltage is applied to the pixel electrode 18 on the first substrate 20 and a negative (−) voltage is applied to the common electrode 42 on the second substrate 40, the positive (+) charged white particles 74 are moved to the side of the second substrate 40 and the negative (−) charged black particles 76 are moved to the side of the first substrate 20. In this state, when light is incident from the outside, i.e., an upper portion of the second substrate 40, incident light is reflected by the white particles 74, thereby implementing white on the electrophoretic display device.
However, the electrophoretic display device 1 having the foregoing structure in the related art may have the following problems.
First, the method of fabricating an electrophoretic display device in the related art has difficulty in attaching the first substrate to the second substrate.
In the electrophoretic display device 1 in related art, the first substrate 20 and second substrate 40 are individually fabricated, and then the first substrate 20 is attached to the second substrate 40 by the adhesive layer 56 to complete the process. In other words, a thin-film transistor for driving a unit pixel and the pixel electrode 18 for applying an electric field to the electrophoretic layer are formed on the first substrate 20, and the common electrode 42, the electrophoretic layer 60 and the adhesive layer 56 are formed on the second substrate 40, and then the first substrate 20 is attached to the second substrate 40 to complete the process.
However, the unit pixel in a typical electrophoretic display device may be formed with a small size less than 150 micrometer in the height and width thereof, and thus it may be difficult to align the electrophoretic layer to accurately match to the size. If the electrophoretic layer is not accurately aligned with the first substrate formed with a thin-film transistor, then an electric field will not be accurately transferred to electrophoretic particles, thereby causing a driving error.
Second, the method of fabricating an electrophoretic display device in the related art has a complicated fabrication process. The first substrate 20 and the second substrate 40 must be fabricated in a different process, and then transferred by a transfer means and attached to each other in the attachment process, thereby causing a delay during the fabrication process and increasing the fabrication cost.
Third, electrostatic discharge generated during the process of attaching the first substrate to the second substrate may cause failure in the initial alignment of electrophoretic particles.
The common electrode 42 and the electrophoretic layer 60 are formed on the second substrate 40, and the adhesive layer 56 is applied to the electrophoretic layer 60. Furthermore, a protection layer is adhered to the adhesive layer 56 in order to prevent the adhesive force of the adhesive layer 56 from being reduced and prohibit foreign materials from being adhered to the adhesive layer 56. However, the protection layer should be peeled off from the second substrate 40 to adhere the second substrate 40 to the first substrate 20, but during the process of peeling off the protection layer, electrostatic discharge may be generated, and as a result, the generated electrostatic discharge may cause misalignment in the initial alignment of electrophoretic particles. The misalignment of electrophoretic particles due to the electrostatic discharge may cause comb-tooth-shaped moiré during the operation of the electrophoretic display device.